Download "Endlers Guppies" assignment

NAME ___________________________ PERIOD ____ DATE ______
“Endler’s Guppies” -- A Reading on Scientific Inquiry
The excerpt you are to read for this assignment is from the book, The Beak
of the Finch: A Story of Evolution in our Time. Most of this book focuses on the
work of Peter and Rosemary Grant who have been studying the finches on the
Galapagos Islands off of South America. However, this eight-page excerpt
describes the work of John Endler with guppies in northern South America and
some islands in the Caribbean Sea.
The reading will not only provide a wonderful example of how natural
selection operates, but it will also describe how a scientist does his work. The
questions below will guide you through the reading and help you to focus on ways in
which John Endler tried to answer some basic questions about the evolution of
guppies.
One thing you will be asked to do throughout the assignment is to ask
questions of the text you are reading. Asking questions is how most of scientific
exploration begins. As you ask questions you are doing exactly what scientists do
every day.
Prior Knowledge
Before you begin this reading, you should make sure you understand the
following ideas:
 Natural selection is the process by which individuals that are better suited
to their environment survive and reproduce most successfully.
 Sexual selection is a special form of natural selection based on an organism’s
ability to mate.
Part I Read paragraphs 1-10
1. Pose a question you have about the description of the guppies given in
paragraph three.
2. Make a hypothesis about why only male guppies have spots.
3. What appears to be the function of the spots on the guppies?
4. Why is natural selection more intense in the lower reaches of the stream?
5. Paragraph ten describes in some detail one of the first things Endler did
once he decided to study the guppies. What did he do? Why did he do this?
Summary: The first two-pages of this reading introduce you to John Endler and
the guppies of Venezuela and three Caribbean islands. How would you describe to
someone how Endler started his research on the guppies?
Part II Read paragraphs 11-15
6. After Endler accurately recorded in great detail the color, size, and position
of the spots on the male guppies, what pattern did his analysis discover?
7. What conclusion does Endler come to in paragraph 14?
8. In the next paragraph, Endler poses an important question. Before moving
on in the reading, how would you respond to this question?
Part III Read paragraphs 16-21
9. How does Endler answer the question posed in paragraph 15?
10. How do male guppies with small dots attract females and yet seem to escape
their predators?
11. What is an interesting pattern of color that seems to support the idea that
natural selection is at work in the guppies?
11. What questions do you have at this point in the reading?
Part IV Read paragraphs 22-33
13. Paragraphs 22-26 describe the evolutionary experiment which Endler set up
in his laboratory at Princeton University in New Jersey. What important steps
did Endler take in designing his experiment?
14. What did he predict would happen?
15. Paragraph 30 describes another important thing scientists must do if they
are to successfully test their hypotheses. What is it?
16. Paragraph 33 raises a doubt about Endler’s results—what is the doubt? Do
you think it is reasonable? Explain.
Part V Read paragraphs 34-40
17. Describe briefly the experiment in nature which Endler designed?
18. How does natural selection and sexual selection contribute to the great
diversity of patterns observed in nature?
19. What is Endler now doing to try to more deeply understand how the guppies
evolve?
20. As you finish this reading, what questions do you still have about how
evolution works in guppies?
21. Take one of the questions you posed in #20. How would you go about
researching this question?
Written by Larry Wakeford as part of Project ARISE, a SEPA-funded project of
the National Institutes of Health, 2008.